Washing machine and method to control the same

ABSTRACT

A washing machine having a plurality of washing units to separately wash laundry according to quantity and type of the laundry, and a method to control the same. In the washing machine having the plurality of washing units to separately wash laundry having different quantities and types, when the plurality of washing units are being simultaneously operated, a current load value of one of the washing units is detected through monitoring of a power line, to thereby determine the operation state of the washing unit. Therefore, the operation of the other washing unit may be controlled so that the power limit is not exceeded. As a result, the plurality of washing units may be operated simultaneously within the range of allowable power capacity of the installation place of the washing machine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.2009-0076656, filed on Aug. 19, 2009 in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein by reference.

BACKGROUND

1. Field

Embodiments relate to a washing machine having a plurality of washingunits capable of separately washing laundry in accordance with quantityand type of laundry, and a method to control the same.

2. Description of the Related Art

A washing machine, generally, a drum-type washing machine is anapparatus equipped with a washing tub to wash contaminated washingobjects (hereinafter, referred to as ‘laundry’) using water anddetergent. The washing machine may perform washing through a series ofoperations including a washing operation in which the laundry is putinto the washing tub and dirt is separated from the laundry by watercontaining detergent, that is, a wash water, a rinsing operation inwhich foam and residual detergent are rinsed off the laundry by waternot containing detergent, that is, a rinse water, and a spin-dryingoperation in which the washed laundry is spin-dried at a high speed.

Some types of laundry should not be washed together in one washing tubbecause of their different characteristics and materials. With a generalwashing machine having one washing tub, such different types of laundrythat cannot be washed together need to be washed separately. Therefore,it becomes cumbersome to wash the laundry separately and operate thewashing machine several times, for example, at least twice, which alsocauses waste of time and energy. Furthermore, when the washing tub has alarge capacity, the large washing tub needs to be wholly operated towash even a small quantity of laundry, thereby causing waste of electricpower.

Recently, some people having sufficient purchasing power use two washingmachines of different capacities such as a large capacity and a smallcapacity. However, in this case, the power capacity required to operatethe two washing machines, for example two heaters, simultaneously mayexceed allowable power capacity of the place in which the two washingmachines are installed.

SUMMARY

Therefore, it is an aspect to provide a washing machine having aplurality of washing units to separately wash different quantities andtypes of laundry, and enabling simultaneous operation of the pluralityof washing units within the allowable power capacity of an installationplace of the washing machine, and a method to control the same.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the embodiments.

In accordance with one aspect, a washing machine includes a plurality ofwashing units; a power connection unit provided to any one of thewashing units to share electric power with the other washing unit; and apower control device which monitors a power line of the other washingunits and thereby controls the operation of the washing unit having thepower control device so that the total power capacity of the pluralityof washing units does not exceed a power limit, when the plurality ofwashing units are simultaneously operated.

The power control device may include a current sensor monitoring thepower line of the other washing unit through the power connection unit,thereby detecting current load value; and a control unit determining theoperation state of the other washing unit based on the detected currentload value and accordingly controlling the operation of the washing unithaving the power control device.

The power control device may be provided to any one of the plurality ofwashing units and connected to the other washing unit not having thepower control device through the power line.

The washing machine may further include a plurality of control unitseach provided to the plurality of washing units to independently controlthe operations of the washing units. Any one of the plurality of controlunits may be connected to the power control device.

The plurality of washing units may be operated independently from oneanother or in connection with one another.

The plurality of washing units may include any one of a drum-typewashing machine and a full-automatic washing machine.

The plurality of washing units may include washing machines of differentcapacities being accumulated in an up and down direction.

The plurality of washing units may include washing machines of differentcapacities arranged side by side.

In accordance with another aspect, a method to control a washing machinehaving a first washing unit and a second washing unit includesconnecting a power supply of the first washing unit to the secondwashing unit; and monitoring a power line of the first washing unit andthereby controlling the operation of the second washing unit so that apower limit is not exceeded, when the first and the second washing unitsare simultaneously operated.

The connecting may be performed by connecting a power cord of the firstwashing unit to a power connection unit of the second washing unit.

The monitoring may include detecting a current load value of the firstwashing unit; and determining whether the power limit is exceeded, bymonitoring the operation state of the first washing unit based on thecurrent load value.

The determining may be performed by determining whether the total powercapacity of the first and the second washing units is equal to orgreater than the power limit when the washing units are beingsimultaneously operated.

The first and the second washing units may be simultaneously operated ifthe total power capacity of the first and the second washing units isless than the power limit.

The operation of the second washing unit may be controlled if the totalpower capacity of the first and the second washing units is equal to orgreater than the power limit.

The controlling of the operation of the second washing unit may beperformed so that the power limit is not exceeded when the first and thesecond washing units are simultaneously driving heaters thereof.

The controlling of the operation of the second washing unit may beperformed in a manner that driving of the heater is delayed or otherwashing functions such as soaking are performed although the heaterneeds to be driven.

The method may further include monitoring the operation state of thefirst washing unit during control of the operation of the second washingunit so as to determine whether the total power capacity is less thanthe power limit; and performing a simultaneous operation of the firstand the second washing units when the total power capacity is less thanthe power limit.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects of the invention will become apparent andmore readily appreciated from the following description of theembodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a perspective view showing the structure of a washing machine;

FIG. 2 is a sectional view showing the structure of the washing machine;

FIG. 3 is a control system view of the washing machine;

FIG. 4 is a structure block diagram of a power control device of thewashing machine;

FIG. 5 is a current waveform view of the power control device of thewashing machine;

FIG. 6 is a flowchart illustrating the control operations of the washingmachine; and

FIG. 7 is a perspective view showing the structure of a washing machine.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments, examples ofwhich are illustrated in the accompanying drawings, wherein likereference numerals refer to like elements throughout.

FIG. 1 is a perspective view showing the structure of a washing machineaccording to an embodiment.

Referring to FIG. 1, the washing machine 10 includes a plurality of, forexample two, washing units 11 and 12 which may be operated independentlyfrom each other or in connection with each other. For example, theplurality of washing units 11 and 12 are arranged vertically in a mannerthat a first washing unit 11 having a large capacity such as 13 kg isdisposed at the lower part and a second washing unit 12 having a smallcapacity such as 3 kg is disposed at the upper part. That is, thewashing machine 10 having the plurality of washing units 11 and 12 isinstalled by accumulatively mounting the second washing unit 12 on anupper surface 13 of the first washing unit 11.

In other words, the first and the second washing units 11 and 12 may bepurchased by a user as independent washing machines. Therefore, thefirst and the second washing units 11 and 12 may be purchased togetheror separately as necessary, and applied in a manner that the secondwashing unit 12 is mounted on the upper surface 13 of the first washingunit 11.

The first and the second washing units 11 and 12 may have the samecapacity. However, it is exemplary that the washing units 11 and 12 aredivided into a large capacity washing unit and a small capacity washingunit considering that the washing machine 10 is characterized by havingthe plurality of washing units 11 and 12. In this case, asaforementioned, even a small quantity of laundry, especially for steamcleaning, can be washed efficiently by operating only the second washingunit 12 having a small capacity. Therefore, waste of power may beprevented.

The washing units 11 and 12 respectively include doors 21 and 22 throughwhich laundry is inserted, input units 31 and 32 to input the user'scommand related to the operations thereof, and display units 41 and 42to display the operation states.

The input units 31 and 32 may each include a power button, a start/stopbutton to start and stop the operation of a corresponding one of thewashing units 11 and 12, a washing unit selection button to select oneor more of the plurality of, for example two, washing units 11 and 12 toperform independent washing/drying operations, and a course and functionbutton to select a washing course and a washing function of thecorresponding one of the washing units 11 and 12. However, the inputunits 31 and 32 may have various other structures, and are not limitedby this embodiment.

According to the embodiment, the input units 31 and 32 and the displayunits 41 and 42 are separately provided to the washing units 11 and 12,respectively. However, an input unit and a display unit may each beprovided in an integrated form.

In addition, detergent supply units 51 and 52 are disposed at a leftupper end and a left middle of the washing machine 10 with respect tothe drawing, to supply detergent to the washing units 11 and 12,respectively.

Although the detergent supply units 51 and 52 are separately formed forthe plurality of washing units 11 and 12 in this embodiment, a singleintegrated detergent supply unit may be provided, by having a pluralityof separate paths to supply detergent to the washing units 11 and 12.Also, mounting positions of the detergent supply units 51 and 52 are notlimited to those described above but may be varied according to theuser.

The washing units 11 and 12 further include first and second power cords61 and 62, respectively, to supply electric power to the washing units11 and 12. The second washing unit 12 is equipped with a power controldevice 400 to share the power supply with the first washing unit 11 andthereby control the operation of the second washing unit 12.

FIG. 2 is a sectional view showing the structure of the washing machineaccording to the embodiment.

Referring to FIG. 2, the first and the second washing units 11 and 12 ofthe washing machine 10 respectively include first and second washingtubs 71 and 72 therein to separately wash laundry according to quantityand type of the laundry. The other basic structures of the first and thesecond washing units 11 and 12 are equivalent to each other.

First and second cylindrical drums 81 and 82 each having a plurality ofholes are rotatably mounted in the first and the second washing tubs 71and 72. First and second motors 101 and 102 are mounted at outer rearparts of the first and the second washing tubs 71 and 72, respectively,as driving devices which rotate first and second rotational shafts 91and 92 connected to the first and second drums 81 and 82 so as toperform washing, rinsing and spin-drying operations. Motors and drivingbelts may be provided instead of the first and the second motors 101 and102. Also, the washing tubs 71 and 72 may be simultaneously orindependently operated using other driving methods such as a clutch.

First and second wash heaters 111 and 112 are mounted at inner lowerparts of the first and the second washing tubs 71 and 72, respectively,to heat water present in the first and the second washing tubs 71 and72. First and second water supply devices 121 and 122 are mounted atupper parts of the first and the second washing tubs 71 and 72,respectively, to supply wash water or rinse water to the washing tubs 71and 72. The first and the second water supply devices 121 and 122include first and second water supply pipes 121 a and 122 a, and firstand second water supply valves 121 b and 122 b. The first and the secondwater supply pipes 121 a and 122 a connect an external water supply pipe130 with the first and the second detergent supply units 51 and 52 sothat wash water or rinse water is supplied into the first and the secondwashing tubs 71 and 72. The first and the second water supply valves 121b and 122 b are mounted on the first and the second water supply pipes121 a and 122 a to control supply of water. According to this structure,the water is passed through the first and the second detergent supplyunits 51 and 52 before being supplied into the first and the secondwashing tubs 71 and 72. Therefore, detergent stored in the first and thesecond detergent supply units 51 and 52 is supplied to the first and thesecond washing tubs 71 and 72 along with the water.

In addition, the first and the second washing units 11 and 12 furtherinclude first and second drying devices 201 and 202, respectively, todry the laundry in the first and the second washing tubs 71 and 72. Thefirst and the second drying devices 201 and 202 respectively includefirst and second drying ducts 211 and 212 disposed at upper parts of thefirst and the second washing tubs 71 and 72 to supply hot air into thefirst and the second washing tubs 71 and 72, first and second condensingducts 221 and 222 mounted at the rear parts of the first and the secondwashing tubs 71 and 72 to remove steam generated during the dryingprocess, and first and second drying heaters 231 and 232 and first andsecond drying fans 241 and 242 mounted in the respective drying ducts211 and 212 to supply the hot air.

Although the first and the second washing tubs 71 and 72 respectivelyhave the first and the second drying devices 201 and 202 to dry thelaundry therein according to this embodiment, a drying device may beprovided at any one of the first and the second washing units 11 and 12considering the structure of the washing machine 10.

The first and the second washing units 11 and 12 further include firstand second drain devices 301 and 302, respectively, to discharge thewater from the insides of the first and the second washing tubs 71 and72. The first and the second drain devices 301 and 302 include first andsecond drain pipes 311 and 312 connected to lower parts of the first andthe second washing tubs 71 and 72 to guide the water to the outside, andfirst and second drain pumps 321 and 322 mounted to the first and thesecond drain pipes 311 and 312, respectively. The drain devices 301 and302 are respectively in fluid communication with an external drain pipe330.

According to this embodiment, the first and the second drain pumps 321and 322 are separately provided to drain water from the first and thesecond washing tubs 71 and 72. However, considering the structure of thewashing machine 10, the second washing tub 72 disposed at the upper partmay have a drain valve such that the water in the second washing tub 72is drained by gravity.

FIG. 3 is a control system view of the washing machine according to theembodiment. The first washing unit 11 further includes a first powersupply unit 501, a first control unit 601, and a first driving unit 701.The second washing unit 12 further includes the power control device400, a second power supply unit 502, a second control unit 602, and asecond driving unit 702.

The first and the second power supply units 501 and 502 supply electricpower applied through power lines to the first and the second washingunits 11 and 12, respectively.

The first and the second control units 601 and 602 may include a microcomputer that controls the overall operations of the washing units 11and 12, including washing, rinsing, spinning and drying, in accordancewith operation data input through the input units 31 and 32.

According to driving control signals from the first and the secondcontrol units 601 and 602, the first and the second driving units 701and 702 drive the first and the second motors 101 and 102, the first andthe second wash heaters 111 and 112, the first and the second watersupply valves 121 and 122, the first and the second drying heaters 231and 232, the first and the second drying fans 241 and 242, and the firstand the second drain pumps 321 and 322, respectively.

The power control device 400 provided to the second washing unit 12connects the power supply of the first washing unit 11 to the secondwashing unit 12 to share the power supply with the first washing unit11. Therefore, the power control device 400 monitors the operation stateof the first washing unit 11 so that the total power capacity of thefirst and the second washing units 11 and 12 does not exceed anallowable power capacity.

FIG. 4 is a structure block diagram of the power control deviceaccording to the embodiment, and FIG. 5 is a current waveform view ofthe power control device.

Referring to FIG. 4, the power control device 400 includes a powerconnection unit 410 connected with the first power cord 61 of the firstwashing unit 11 to connect the power supply of the first washing unit 11to the second washing unit 12, a current sensor 420 connected to a powerline 411 of the first washing unit 11 to detect a current load value ofthe power line 411, and a voltage conversion part 430 to convert thecurrent load value detected by the current sensor 420 into a voltagevalue and transmit the voltage value to the second control unit 602 ofthe second washing unit 12.

Referring to FIG. 5, the current sensor 420 monitors the operation stateof the first washing unit 11 and accordingly generates a predeterminedcurrent at a second side thereof proportional to a current of a firstside. The second control unit 602 may determine the operation state ofthe first side of the current sensor 420, that is, the first washingunit 11 using the current generated at the second side of the currentsensor 420.

The power conversion part 430 may be a general voltage conversioncircuit including resistors 431 and 432, a diode 433 and a condenser434.

When the first and the second washing units 11 and 12 are beingsimultaneously operated, the second control unit 602 of the secondwashing unit 12 monitors the operation state of the first washing unit11 based on the current load value detected by the current sensor 420and accordingly controls the operation of the second washing unit 12 sothat the first and the second washing units 11 and 12 are operatedwithin the allowable capacity range.

According to the above-described embodiment, the power control device400 is formed at the second washing unit 12 to monitor the operationstate of the first washing unit 11 and the operation of the secondwashing unit 12 is controlled so that the power limit is not exceededduring the simultaneous operation of the first and the second washingunits 11 and 12. However, embodiments of the present invention are notlimited to this. For example, the power control device 400 may be formedat the first washing unit 11 to monitor the operation state of thesecond washing unit 12 and accordingly control the operation of thefirst washing unit 11 so that the power limit is not exceeded during thesimultaneous operation.

Here, the simultaneous operation of the first and the second washingtubs 71 and 72 may be performed in various manners. For example, both ofthe first and the second washing tubs 71 and 72 may be supplied withlaundry and operated simultaneously. In another case, after one of thefirst and the second washing tubs 71 and 72 is supplied with laundry andoperated, the other one may be next supplied with laundry and operatedwhile the former one is operating.

Hereinafter, the operational processes and effects of theabove-structured washing machine will be described.

FIG. 6 is a flowchart illustrating the control operations of the washingmachine to perform the simultaneous operation of the first and thesecond washing units 11 and 12 which are capable of separately washingdifferent quantities and types of laundry, such that the power limit isnot exceeded during the simultaneous operation.

First, laundry is classified according to quantity or type and isseparately put into the first and the second washing tubs 71 and 72 ofthe first and the second washing units 11 and 12. When the user selectsthe washing courses and functions corresponding to the washing tubs 71and 72, the operation data selected by the user is input to the firstand the second control units 601 and 602 through the first and thesecond input units 31 and 32, respectively.

Here, the first power cord 61 of the first washing unit 11 is connectedto the power connection unit 410 of the power control device 400provided to the second washing unit 12 (operation S800) so that thesimultaneous operation of the first and the second washing units 11 and12 is performed within the allowable power capacity.

The first and the second control units 601 and 602 determine whether thefirst and the second washing units 11 and 12 are being simultaneouslyoperated (operation S802). When it is determined that the simultaneousoperation is being performed, the power control device 400 monitors thepower line 411 of the first washing unit 11 through the current sensor420, thereby detecting the current load value of the first washing unitas shown in FIG. 5 (operation S804).

The current load value detected by the current sensor 420 is convertedinto a voltage value by the voltage conversion part 430 and then inputto the second control unit 602 of the second washing unit 12.

Accordingly, the second control unit 602 monitors the operation state ofthe first washing unit 11 using the second side current of the currentsensor 420 input through the voltage conversion part 430 (operationS806) and determines whether the total power capacity of the first andthe second washing units 11 and 12 is equal to or greater than the powerlimit (operation S808).

Here, the power limit refers to a predetermined maximum value of powerdefined so as not to exceed the allowable power capacity in generalhomes. In an electric appliance including a combination of at least twodevices, the total power capacity should not exceed the power limit evenwhen the devices are operating simultaneously.

When the total power capacity of the first and the second washing units11 and 12 is less than the power limit as a result of the determinationin operation S808, the first and the second washing units 11 and 12 aresimultaneously operated (operation S810) and the process is fed back tooperation S804 to continue monitoring the operation state of the firstwashing unit 11.

If the total power capacity of the first and the second washing units 11and 12 is equal to or greater than the power limit as a result of thedetermination in operation S808, the operation of the second washingunit 12 is controlled (operation S812).

The operation of the second washing unit 12 may be controlled in amanner that the second wash heater 112 or the second drying heater 232of the second washing unit 12 may be kept on standby while the firstwash heater 111 or the first drying heater 231 of the first washing unit11 is in operation. During this, for example, other washing functionssuch as soaking may be performed although the second wash heater 112 orthe second drying heater 232 needs to be driven. Accordingly, the firstand the second washing unit 11 and 12 may be simultaneously operatedwithin the range of the allowable power capacity.

It is determined whether the total power capacity of the first and thesecond washing units 11 and 12 is less than the power limit as thewashing function of the second washing unit 12 is controlled (operationS814). When the total power capacity is less than the power limit, theprocess is fed back to operation S810 so that the first and the secondwashing units 11 and 12 are simultaneously operated.

If the total power capacity is not less than the power limit as a resultof the determination of operation S814, the process is fed back tooperation S812 and subsequent operations are performed.

FIG. 7 is a perspective view showing the structure of a washing machineaccording to another embodiment.

Referring to FIG. 7, the washing machine 10 according to anotherembodiment of the present invention includes the plurality of, forexample two, washing units 11 and 12 which may be operated independentlyfrom each other or in connection with each other. The washing units 11and 12 are arranged side by side, for example, in a manner that thefirst washing unit 11 having a large capacity such as 13 kg is disposedon the left while the second washing unit 12 having a small capacitysuch as 3 kg is disposed on the right with respect to the drawing.

Therefore, the user may purchase the first and the second washing units11 and 12 separately as independent washing machines. That is, the firstand the second washing units 11 and 12 may be purchased together orseparately as necessary, and applied by being arranged side by side.

In the embodiment shown in FIG. 1 as well, the first power cord 61 ofthe first washing unit 11 is connected to the power connection unit 410of the power control device 400 provided to the second washing unit 12so that the simultaneous operation of the first and the second washingunits 11 and 12 is performed within the range of the allowable powercapacity.

If a general washing machine without the power control device 400 isnewly purchased in addition to the existing second washing unit 12having the power control device 400, a power supply of the generalwashing machine may be monitored by the second washing unit 12 byconnecting a power cord of the general washing machine. Accordingly, thefirst and the second washing units 11 and 12 may be simultaneouslyoperated within the range of allowable power capacity.

On the other hand, when the second washing unit 12 having the powercontrol device 400 is purchased in addition to an existing generalwashing machine without the power control device 400, the power supplyof the general washing machine may be monitored by the second washingmachine 12 by connecting a power cord of the second washing unit 12.Accordingly, the first and the second washing units 11 and 12 may besimultaneously operated within the range of allowable power capacity.

Furthermore, although the washing units 11 and 12 both have beenexplained as drum-type washing machines in the embodiments, the presentinvention is not limited to the disclosed embodiments. The same purposeand effect may be achieved when the first and the second washing units11 and 12 are both full-automatic washing machines, or a drum-typewashing machine and a full-automatic washing machine.

As is apparent from the above description, in a washing machine having aplurality of, for example two, washing units to separately wash laundryhaving different quantities and types, when the plurality of washingunits are being simultaneously operated, a current load value of one ofthe washing units is detected through monitoring of a power line, tothereby determine the operation state of the washing unit. Therefore,the operation of the other washing unit may be controlled so that thepower limit is not exceeded. As a result, the plurality of washing unitsmay be operated simultaneously within the range of allowable powercapacity of the installation place of the washing machine.

Although a few embodiments have been shown and described, it would beappreciated by those skilled in the art that changes may be made inthese embodiments without departing from the principles and spirit ofthe invention, the scope of which is defined in the claims and theirequivalents.

What is claimed is:
 1. A washing machine comprising: a plurality ofwashing units; a power connection unit provided to any one of thewashing units to share electric power with the other washing unit; and apower control device to monitor a power line of the other washing unitsand control the operation of the washing unit having the power controldevice so that the total power capacity of the plurality of washingunits does not exceed a power limit, when the plurality of washing unitsare simultaneously operated.
 2. The washing machine according to claim1, wherein the power control device comprises: a current sensor tomonitor the power line of the other washing unit through the powerconnection unit, thereby detecting current load value; and a controlunit to determine the operation state of the other washing unit based onthe detected current load value and accordingly control the operation ofthe washing unit having the power control device.
 3. The washing machineaccording to claim 2, wherein the power control device is provided toany one of the plurality of washing units and connected to the otherwashing unit not having the power control device through the power line.4. The washing machine according to claim 1, further comprising aplurality of control units each provided to the plurality of washingunits to independently control the operations of the washing units. 5.The washing machine according to claim 4, wherein any one of theplurality of control units is connected to the power control device. 6.The washing machine according to claim 1, wherein the plurality ofwashing units are operated independently from one another or inconnection with one another.
 7. The washing machine according to claim6, wherein the plurality of washing units comprise any one of a drumwashing machine and a full-automatic washing machine.
 8. The washingmachine according to claim 6, wherein the plurality of washing unitscomprise washing machines of different capacities arranged vertically.9. The washing machine according to claim 6, wherein the plurality ofwashing units comprise washing machines of different capacities arrangedhorizontally.
 10. A method to control a washing machine having a firstwashing unit and a second washing unit, the method comprising:connecting a power supply of the first washing unit to the secondwashing unit; and monitoring a power line of the first washing unit andthereby controlling the operation of the second washing unit such that apower limit is not exceeded, when the first and the second washing unitsare simultaneously operated.
 11. The method according to claim 10,wherein the connecting is performed by connecting a power cord of thefirst washing unit to a power connection unit of the second washingunit.
 12. The method according to claim 10, wherein the monitoringcomprises: detecting a current load value of the first washing unit; anddetermining whether the power limit is exceeded, by monitoring theoperation state of the first washing unit based on the current loadvalue.
 13. The method according to claim 12, wherein the determining isperformed by determining whether the total power capacity of the firstand the second washing units is equal to or greater than the power limitwhen the washing units are being simultaneously operated.
 14. The methodaccording to claim 13, wherein the first and the second washing unitsare simultaneously operated if the total power capacity of the first andthe second washing units is less than the power limit.
 15. The methodaccording to claim 13, wherein the operation of the second washing unitis controlled if the total power capacity of the first and the secondwashing units is equal to or greater than the power limit.
 16. Themethod according to claim 15, wherein controlling the operation of thesecond washing unit is performed so that the power limit is not exceededwhen the first and the second washing units are simultaneously drivingheaters thereof.
 17. The method according to claim 16, whereincontrolling the operation of the second washing unit includes delayingdriving of the heater and performing other washing functions includingsoaking while the driving of the heater is delayed.
 18. The methodaccording to claim 17, further comprising: monitoring the operationstate of the first washing unit during control of the operation of thesecond washing unit so as to determine whether the total power capacityis less than the power limit; and performing a simultaneous operation ofthe first and the second washing units when the total power capacity isless than the power limit.
 19. A washing machine comprising: a firstwashing unit and a second washing unit; a power connection unit providedin one of the first and second washing units to share electric powerwith the other washing unit; and a power control device to monitor apower line of the other washing unit and to control the operation of thewashing unit having the power control device wherein the power controldevice controls total power consumption of the first and second washingunits to stay below a predetermined power limit.
 20. The washing machineaccording to claim 19, wherein the first washing unit has a capacity ofapproximately 13 kg, and the second washing unit has a capacity ofapproximately 3 kg.